The instant invention relates to a method of injecting tubing down a pipe or open hole. In particular, the instant invention relates to a method of injecting coiled tubing down a pipe in deep water to service the pipeline, i.e., to remove paraffinic blockages, hydrates, scale, or solid debris from the pipe. More particularly, the instant invention relates to a method of injecting tubing into a pipe where a substantial portion of the pipe is horizontal and the total injected length is greater than about 6,000 feet (1,830 meters).
In the development and production of subterranean hydrocarbon deposits and other energy sources there are many occasions when it is necessary to insert an elongated tube from the surface deep into a pipe or open hole. These pipes or holes may be vertical, horizontal, curved, or combinations of these and may be part of, for example, a well, pipe line, production line, or drill pipe. The inserted tube has an outer diameter that is smaller than the inner diameter of the pipe or open hole. The insertion of the tube may be for purposes of, for example, removing blockages or general servicing.
Often during repair or servicing of a pipe a rig capable of handling long lengths of straight screw-type pipes is not available. In many cases the strength of larger diameter straight screwed tubing is not needed so the cost of running this type of tube is not justifiable. In these cases it is often advantageous to use a long, continuous injected tubing called coiled tubing. Many apparatuses have been developed to insert or inject a continuous length of relatively thin walled steel tubing into a pipe or open hole from a large reel or spool on the surface.
Large forces are often necessary to insert and withdraw thousands of feet or more of steel tubing into a pipe or open hole which may be filled with hydrocarbons or other materials. Most current apparatuses focus on the injector head located where the smaller tubing is injected into the larger tubing. The injector head grips the tubing along its length and, in conjunction with a motor, guides and forces the tubing into the pipe via, for example, a dual, opposed conveyor belt on the surface of the well. Typical injector heads are described in, for example, U.S. Pat. Nos. 3,827,487; 5,309,990; 4,585,061; 5,566,764; and 5,188,174. These patents are incorporated here by reference.
Unfortunately, the apparatuses of these patents are problematic in many respects. One problem is that the tubing may be bent or kinked, i.e., the tubing becomes helical, down the well due to the large forces pushing against it and the weight of the tubing itself. This is especially problematic when the pipe is deviated from vertical. As the pipe becomes more horizontal, the weight of the coiled tubing itself no longer acts as a force pulling the tubing along, but instead acts against the wall of the pipe, creating friction. In addition, the weight of the tube no longer acts to straighten the coiled tubing, and the coil encourages coiling in the pipe. This coil, coupled with friction, results in increased force between the coiled tube and the inner diameter of the pipe and effectively binds the tubing. As a result of this and other problems, such prior art devices cannot effectively insert more than about 3,000 to about 5,000 feet (900 to 1500 meters) of tubing in substantially horizontal pipe.
Another typical problem with prior art devices is that the injector equipment associated with such devices is often relatively heavy, difficult to move, and complex due to a large chain assembly of machinery that serves as a conveyor belt to force the tubing into the pipe.
One method of reducing friction in injected tubing is the tubing friction reducer described in U.S. Pat. No. 5,692,563. This patent describes a friction reducer containing multiple bearings set in legs extending outward from a body. The patent specifies that bearings of about 0.2188 inches in diameter can be used. Use of these bearings would give a clearance of about 0.1 inches or less between the tip of the bearing and the holding leg. In addition, this patent describes friction reducing devices with 12 or more rows of wheels. Applicants found that the described friction reducer embodiments were not applicable for larger diameter coiled tubing, in that the designs did not have the mechanical strength needed to support tubing. For example, the patent states that the friction reducer could be made of a metal such as aluminum, plastic, rubber, or other composites, and the ball bearings in one embodiment are of Teflon. Applicants found that molded steel bodies with a minimum number of welds were necessary to circumvent tight turns in a pipe without breaking. Applicants found certain very durable composites, such as polysulfone, could be used as wheel material only for very light service. For normal service, steel wheels are required. Finally, applicants found that sludge and oil in a pipeline would freeze the bearings described in the ""563 patent. Conventional testing assumes a relative high contact stress with the oil lubricity assisting, but with the oil viscosity as a non-factor. In the low-loading characteristics of coiled tubing, the viscosity can be a factor several times that of friction. Therefore, the devices described in U.S. Pat. No. 5,692,563 were not deemed operable for heavier coiled tubing or for pipe with obstructions.
Other methods have been employed to increase the length to which tubing can be injected. U.S. Pat. No. 5,704,393 describes an apparatus that can be set in the well at the end of the coiled tubing string at a determinable location. The apparatus is a valve apparatus, a packer apparatus, and a connector. Seals allow the coiled tubing, but not fluid, to move in a centrally located bore through the packer apparatus. The apparatus is immobile against the outer pipeline, and has the ability restrict or prevent fluid flow. Once the packer is set, the annular pressure, i.e., the pressure differential between the pipeline and the interior of the coiled tubing, is increased by injecting fluid into the annular volume. This increased pressure stiffens and straightens the coiled tubing, allowing for increased distance of injection of coiled tubing into the pipeline.
It is apparent that what is needed in the art is a method for readily inserting and withdrawing tubing from a pipe for long distances, i.e., greater than about 6,000 feet (1830 meters), without bending or kinking the tubing. It would be beneficial if such a method could be employed to insert and withdraw tubing from a substantially horizontal pipe of extended length of greater than 6,000 feet (1830 meters), and that the tubing can extend past turns. Moreover, it would be of great benefit if such an apparatus was portable, easily handled, and could be adapted to handle tubing of differing diameters.
A new method has been developed for inserting and withdrawing tubing from pipes or open holes. Beneficially, the new method may be employed to insert and withdraw tubing to lengths of over 6000 feet (1830 meters), preferably greater than 26,000 feet (9900 meters), and more preferably greater than 60,000 feet (18,300 meters). Advantageously, the method uses an apparatus that is portable, easily handled, and adaptable to handle tubing of differing diameters.
The method comprises feeding a coil tubing into a pipe that has a larger diameter than the coil tubing. The injected tubing has a thruster pig located at or near the distal end of the injected tubing. The thruster pig utilizes a pressure differential across the thruster pig to generate force needed to inject tubing down a pipe or well. The thruster pig device is attached to the tubing, and is as a practical matter usually attached near, i.e., within about 2000 feet, preferably within 100 feet, of the distal end of the tubing. The body of the thruster pig has a outer diameter greater than the outer diameter of the injected tubing and equal to or smaller than the inner diameter of the pipe. The thruster pig has a sealing apparatus, for example one or more chevrons, to impede fluid migration between the body of the thruster pig and the inner surface of the pipe. This effectively creates an annulus between the injected tubing and the pipe so pressure can be applied to the rear of the thruster pig. The thruster pig has an attaching apparatus for attaching the device to the end of the small diameter tubing or to the exterior of the small diameter tubing. The thruster pig has an opening that allows fluids pumped down the center of the injected tubing to pass to the front of the thruster pig. Finally, the thruster pig has a means for allowing fluids to flow from the annulus through the device as the thruster pig is being withdrawn.
After the thruster pig is inside the pipe, at least a portion of the force needed to inject the tubing into the pipe is provided by pressure exerted on the annulus between the pipe and the injected tube and therefore also exerted on the back of the thruster pig. The pressure differential between the front of the thruster pig and the rear of the thruster pig provides force to inject the tubing into the pipe.
The injected tubing also has one or more skate apparatuses attached to the tubing at predetermined intervals. The skate has a body diameter greater than the diameter of the injected tubing and has a cylindrical port capable of fitting around a portion of the injected tubing. The body opens length-wise by an amount sufficient to insert the injected tubing. This allows the skate apparatus to securely fit around the outer diameter of the injected tubing. There is a means of fastening the skate to the outer diameter of the injected tube. Finally, there is a set of three to six, preferably three to four, rigid arms extending in a plane in a direction toward the interior surface of the pipe. Each of the arms contains one or more wheels on the distal end of the arms. xe2x80x9cIn a planexe2x80x9d means that there is a cross-section of the skate that will include at least a portion of the three to four arms that radiate out from the body. There may be more than one set of three to four arms on a body, provided the sets are displaced axially along the body from one another.
The wheels are capable of movable communication with the inner surface of the pipe. The radius from the center of the injected tubing to the outermost edge of the wheels or rollers is not smaller than 0.5 times the radius of the pipe. The skate maintains a portion of the tubing in the center of the pipe such that the movement-restricting force for at least a portion of the injected tubing is rolling friction rather than a combination of sliding friction and the force needed to overcome the shear viscosity of the fluid within the pipe.
The instant invention also is a method for withdrawing the injected tubing from the pipe. The method comprises opening a normally closed aperture through the body of the thruster pig to allow fluid migration from the annulus to the pipe that is ahead of the thruster pig. Optionally, an equalizing valve can be run in the thruster pig, or the coiled tubing can be opened at the reel to eliminate the annular force on the thruster pig as it is removed from the pipe line or well. In some cases, such as thrusting the coiled tubing into the pipe or well with an electric line inside of the pipe, these valves can be opened or closed using the electric power available.
Optionally, pressure may be exerted through the injected tubing to the pipe ahead of the thruster pig until the pressure is greater than the pressure in the annulus behind the thruster pig. This provides a portion of the force needed to withdraw the injected tubing from the pipe.